1. Field of the Invention
The present invention relates to a wiper for a sewing machine.
2. Description of the Related Art
A wiper for a sewing machine is used to sweep a cut upper thread and pull it out to the upper side of a working cloth and a cloth presser after the working cloth has been completely sewn and the sewing thread has been cut thereunder. The wiper prevents the starting portion of the thread sewn into the succeeding working cloth from becoming slack on the upper side thereof and causing the quality of the working cloth to deteriorate.
Conventional wipers for a sewing machine utilize either one of two methods, i.e., either a forward stroke or a backward stroke wiping method. In the forward stroke method as shown in FIG. 8 the wiper W follows the trace as shown in an arrow a1 and performs a wiping operation when the wiper W proceeds to the rising position from a lowest rest position as shown by a solid line. In the backward stroke wiping method, as shown in FIG. 9 the wiper W follows the trace as shown in an arrow b1 and performs the wiping operation when the wiper W, which is at the highest rest position as shown by a solid line, proceeds to the rising position after lowering. In FIGS. 8 and 9, a hook portion H is formed at the tip end of the wiper W, O is a wiper shaft, F is a surface on which the working cloth is placed, NL is a vertical path of a needle N and NT is an upper thread which is drawn through the working cloth from the needle N.
A hook portion H of a conventional wiper W is shown in FIG. 10, wherein the wiping operation is performed at the concave circular arced surface HD in either of the forward and backward stroke methods.
An operator of the sewing machine employs either of the methods integrally, taking into consideration the specification and condition of sewing the working cloth.
When the forward stroke method is used and the rest position of the wiper W is close to the working cloth, the wiper W sometimes obstructs the sewing operation of some working cloths depending on the shapes and kinds thereof even though the wiper seldom fails to wipe the thread, since it wipes the upper thread NT which is drawn through the working cloth to the vertical path NL of the needle N at the concave circular arced surface HD of the hook portion H as it rises from the lowest rest position.
When the backward stroke method is used the hook portion H sometimes fails to catch the upper thread NT at the concave circular arced surface HD thereof during the backward stroke since the wiper W pushes off the upper thread NT during the lowering process of the forward stroke and thereafter pulls out the same from the working cloth as it rises or the hook portion H hooks the upper thread NT at the convex circular arched surface HV during the forward stroke and pulls out the thread from the working cloth so that it is extended toward the direction contrary to the cloth edge.
If the cut thread is wiped toward the opposite side of the cloth end, the end of the upper thread NT may be sewn into the working cloth as shown in FIG. 7, so that the quality of product deteriorates. Therefore the wiper W generally wipes the thread toward the cloth end in sewing operations.